1. Field of the Industrial Application
The present invention relates to a gas insulated switch gear device used, for example, for a SF.sub.6 gas insulated enclosed type substation, and, in particular, relates to a high speed grounding switch which operates to guarantee the current interrupting performance and the inter-electrode insulation performance of a gas circuit breaker.
2. Conventional Art
The gas insulated switch gear device of the type explained above used for a SF.sub.6 gas insulated enclosed type substation is constituted by such constituent elements as a gas circuit breaker, a disconnecting switch, an arrester and bus lines, and the circuit breaker is designed to open a grounded power transmission line during a failure of the power transmission lines (in particular because of lightning fault) and to interrupt a fault current such as short-circuiting current and grounding fault current.
For power transmission of large capacity, the transmission voltage is high and the electro-static capacities between the power transmission lines (bus lines) of respective phases are also large, such that even after once interrupting a fault phase current as illustrated in FIG. 5 (in FIG. 5 it is assumed that power transmission line c among those of a, b and c experiences a fault phase suffered by lightning and the remaining power transmission lines a and b are sound phases), a duration time of a secondary arc current is prolonged due to an electro-static induction from the sound phases, which renders a high speed reclosing within a time desired for the power transmission system operation difficult. Namely, although the induced lightning surge voltage is reduced by the arrester, a primary arc current (as illustrated by reference A in FIG. 5) flows from the line of fault phase, thereby a surge current as illustrated by reference B is caused to occur on a transmission line of sound phase due to electro-static induction, and due to an electromotive force by the electro-static induction a further electro-static induction as illustrated by reference C is again caused on the transmission line C (fault phase) and induces the secondary arc current.
As a countermeasure to the above problem, a high speed grounding switch has been developed. The high speed grounding switch as illustrated in FIG. 5 operates at a higher speed than the open and close operation of the gas circuit breaker during the open and close operation thereof, in that the high speed grounding switch automatically grounds both ends of the opened transmission line in fault phase and immediately thereafter automatically opens the same (in other words, the high speed grounding switch grounds the transmission line in fault phase after the gas circuit breaker opens for the fault phase and then releases the grounding, and thereafter the gas circuit breaker recloses) such that the current interrupting performance and the inter-electrode insulation performance of the gas circuit breaker are guaranteed.
FIG. 6 shows a specific arrangement as an example of a conventional gas insulated switch gear device to which the above mentioned type of a high speed grounding switch is applied, wherein numeral 40 is a gas circuit breaker, 20 a disconnecting switch, 60 a bus line, 70 an arrester, 80 a bushing and between the gas circuit breaker 40 and the disconnecting switch 20 a high speed grounding switch 10 is disposed. Numeral 24 is a further grounding switch which is designed for different use and performance from those of the high speed grounding switch 10 and operates for guaranteeing the operation of the disconnecting switch 20.
Namely, the high speed grounding switch 10 is required to operate at a high speed for performing a high speed grounding operation and releasing operation thereafter in comparison with the open and close operation of the gas circuit breaker 40 during the open and close operation thereof in order to guarantee the current interrupting performance and the inter-electrode insulation performance of the gas circuit breaker 40 as explained above. On the other hand, the grounding switch 24 (as, for example, disclosed in JP-A-61-170212) for the disconnecting switch 20 is designed to ground the disconnecting switch 20 and to allow the remaining electric charge thereon to discharge toward the ground side when the gas circuit breaker 40 and the disconnecting switch 20 are opened for maintenance and inspection of the gas insulated switch gear device. Therefore, the grounding switch 24 is not required to operate at high speed even if the operation is performed either manually or automatically such that problems encountered in connection with the high speed grounding switch 10, which will be explained hereinafter, are not applicable to the grounding switch 24.
In FIG. 6, when a fault current flows in from a power transmission line via the bushing 80, the arrester 70 and a conductor (center conductor) 61 of the bus line 60, the circuit breaker 40 opens the power transmission line (bus line) for a moment and the movable electrode (movable contact) 11 of the high speed grounding switch 10 is closed at high speed toward the stationary electrode (stationary contact) 13 thereof provided at the conductor portion 61 of the bus line 60 in order to discharge the fault current toward ground.
In the FIG. 6 arrangement, the central axis direction of the conductor 61 of the bus line 60 crosses at right angles with the closing direction of the movable electrode 11 of the high speed grounding switch 10, and further the movable electrode 11 moves at high speed toward the stationary electrode 13 during fault occurrence and the conductor portion 61 is subjected to severe mechanical impact and stress, and the durability of the conductor portion is significantly damaged.
In addition, immediately after the movable electrode 11 is closed to the stationary electrode 13, an extremely large fault current flows therethrough to constitute an electrically closed circuit as illustrated by a broken line in FIG. 6 and an electro-magnetic force is induced between the stationary electrode 21 and the movable electrode 22 of the disconnecting switch 20 and the movable electrode 11 of the high speed grounding switch 10 to thereby cause a stress thereon indicated by an arrow x or x', of which stress damages the durability of the device as well as deteriorates the operating performance of the movable elements 11 and 22.
For this reason, the stationary electrode 21 and the movable electrode 22 of the disconnecting switch 20, and the movable electrode 11 and the conductor 61 provided with the stationary electrode 13 of the high speed grounding switch 10 are required to employ a structure for increasing the mechanical strength which increases the processing cost of their parts and the production cost thereof.
Further, with the above arrangement structure, the high speed grounding switch 10 is accommodated in a sectioned insulation gas chamber between the gas circuit breaker 40 and the disconnecting switch 20 which requires many insulation spacers disposed therebetween. As a result, the possibility of common use of conventional parts thereof is reduced, the size of the parts for constituting the high speed grounding switch 10 increases and the entire installation space for the gas insulated switch gear device also increases.